Pharmacokinetics and tissue concentrations of azithromycin in ball pythons (Python regius)

Abstract

Objective - To determine pharmacokinetics and tissue concentrations of azithromycin in ball pythons (Python regius) after IV or oral administration of a single dose. Animals - 2 male and 5 female ball pythons. Procedures - Using a crossover design, each snake was given a single dose of azithromycin (10 mg/kg) IV. After a 4-week washout period, each snake was given a single dose of azithromycin (10 mg/kg) orally. Blood samples were collected prior to dose administration and 1, 3, 6, 12, 24, 48, 72, and 96 hours after azithromycin administration. Azithromycin was quantitated by use of liquid chromatography-mass spectrometry. Results - After IV administration, azithromycin had an apparent volume of distribution of 5.69 L/kg and a plasma clearance of 0.19 L/h/kg. Harmonic means for the terminal half-life were 17 hours following IV administration and 51 hours following oral administration. Mean residence times were 37 and 94 hours following IV and oral administration, respectively. Following oral administration, azithromycin had a peak plasma concentration (Cmax) of 1.04 μg/mL, a time to Cmax of 8.4 hours, and a prolonged mean absorption time of 57 hours. Mean oral bioavailability was 77%. Tissue concentrations ranged from 4 to 140 times the corresponding plasma concentration at 24 and 72 hours after azithromycin administration. Conclusions and Clinical Relevance - Azithromycin is well absorbed and tolerated by ball pythons. On the basis of plasma pharmacokinetics and tissue concentration data, we suggest an azithromycin dosage in ball pythons of 10 mg/kg, orally, every 2 to 7 days, depending upon the site of infection and susceptibility of the infective organism.